The present invention relates to a filter made of a multilayered filter medium, a method for the manufacture thereof and the use of the filter according to the invention.
The use of filters, particularly of multilayered filter media, has long been known in the art. For example air filters have long been used in the automotive sector, in air conditioning systems, indoor filters, pollen filters, clean-room filters, domestic filters etc. Filters have also long been used for the filtration of fluid media. Examples include oil filters and hydraulic filters.
Depending upon of the area of application the filters are adapted in order to achieve a sufficient filtration efficiency and service life. Thus LEFs (Low Efficiency Filters) are used as pre-filters in air/gas and fluid filtration, while High Efficiency Filters are also used in the area of HEPA (air) or water treatment.    U.S. Pat. No. 5,993,501 discloses multilayered filter media and filters consisting of a rigid pleatable base layer, the actual filter layer and a top layer.    EP-A-0980700 discloses filter media and filters with a gradient structure.    EP-A-0729375 discloses voluminous filter media and filters based on crimped fibres.    EP-A-0789612 discloses compressed filter media and filters based on melt polymers.    EP-A-1313538 discloses voluminous filter media and filters based on crimped fibres and additional microfibres.    EP-A-1378283 also discloses in a general manner multilayered filter media and filters.
The aforementioned known filters and filter media are already well-suited for gas and fluid filtration. There is nevertheless a need for further-improved filters which permit in particular a higher air flow rate and at the same time exhibit a high separation efficiency without an excessive pressure loss being observed.
It has been found in a surprising manner that the known filter media can be significantly improved by the use of special multilayered filter media.